1. Field of the Invention
The present invention relates to a method for estimating reception quality of communication area, apparatus thereof, and program thereof and, more particularly, to a reception quality estimating method for estimating success or failure of handover within a communication area in a mobile communication system.
2. Description of the Related Art
Handover (hereinafter, referred to as “HO” for simplicity) exerts great influence on communication quality in a wireless communication system where mobile users are moving from one place to another. Thus, in designing and operating the wireless communication system, it is preferable to estimate the area (hereinafter, referred to as “HO area”) where HO occurs and to estimate whether the HO fails (hereinafter, the area where HO fails is referred to as “HO failure area”) or succeeds (hereinafter, the area where HO succeeds is referred to as “HO success area”) so as to grasp the HO failure area and HO success area.
If the HO failure area and HO success area can clearly be distinguished from each other, parameter tuning capable of reducing the number of occurrences of faults due to the HO failure can be achieved in designing the wireless communication system. This avoids a trouble that an occurrence of a fault due to the HO failure becomes clear only after the actual operation of the system is started, thereby enabling stable operation.
As a related art of this technical area, there is known an HO area estimating method disclosed in Patent Document 1 (JP-2006-352385-A). This document discloses a method for grasping reception qualities of radio waves from a plurality of base stations at given locations within the service area of a wireless communication system and estimating the HO area based on the reception qualities. To implement this method, a condition for estimating the HO area and condition for estimating an area where a base station which is HO destination is not found and thereby communication becomes unstable are set in this technique.
With this technique, by previously grasping radio propagation characteristics (reception power distribution) of an area for which an occurrence of the HO needs to be confirmed based on a computer simulation or actual measurement, it is possible to estimate the HO area and area where communication becomes unstable.
Processing of HO includes searching an HO destination base station and assignment processing to the found HO destination base station, so that a predetermined time is required to complete the HO processing. Further, a mobile terminal may be moving under such a condition that the HO processing is carried out, so that reception quality always changes. Therefore, the reception quality changes even while the HO processing to switch to a new HO destination base station is carried out with the result that if a radio wave from an HO source base station cannot be received during the HO processing, communication breaks up. This is one of the factors of HO failure.
Further, there may be case where the reception quality of a radio wave from the HO destination base station at the time point when the HO destination base station is determined differs from that during execution of the HO processing or immediately after the execution of the HO processing even in a state where a radio wave from the HO source base station can be received. When the reception quality of a radio wave from the HO destination base station determined at the search time is deteriorated during or immediately after the HO processing, communication may break up, resulting in HO failure.
The technique disclosed in Patent Document 1 does not consider the time required for such HO processing, and the area where the HO occurs is estimated by referring only to the reception quality in the estimated area. More specifically, whether the HO occurs or not is determined based on whether the reception quality of a radio wave from the HO source base station is deteriorated and whether a difference in the reception quality between radio waves from the HO source base station and HO destination base station exceeds a specified value and, here, success or failure of the HO cannot be determined. Further, also as to an area where communication becomes unstable, the technique derives the area by referring only to the reception quality without considering the HO processing time.
The problem of the related art is that it is impossible to estimate success or failure of the HO processing when the HO occurs. This is because that the related art does not consider the time required for the HO processing and, accordingly, does not consider a change with time of the reception quality of a radio wave from the HO source base station and reception quality of a radio wave from the HO destination base station at the HO processing execution time.